1. Field of the Invention
The present invention relates to high-analysis low pH liquid fertilizer compositions, prepared by reacting urea and phosphoric acid or a mixture of phosphoric acid and sulfuric acid, stabilized with small amounts of ammonia.
2. Related Art
Ammonium phosphates and polyphosphates have been prepared by neutralizing wet process phosphoric acid. Various procedures have been employed urea in the production of the ammonium phosphates to complex impurities or as condensing agents to maintain the ammonium phosphates as water soluble for use in liquid fertilizers, for example, U.S. Pat. Nos. 3,022,153 and 3,540,874.
Similarly U.S. Pat. No. 3,723,086 discloses an improved process for producing ammonium phosphates and polyphosphates by dissolving 2 to 10 percent by weight of urea in a stream of wet phosphoric acid prior to ammoniating the wet phosphoric acid. The urea serves to inhibit the formation of insoluble materials. Since wet phosphoric acid contains 15 to 20 weight percent free water, 10 weight percent urea would form a true solution. The ammoniatization is carried out at elevated temperatures, e.g., 200.degree. F. with approximately a molar amount of ammonia.
The high analysis liquid fertilizers which are the subject of the present invention are nonammoniated. They are are the reaction product of urea and phosphoric acid or a mixture of phosphoric acid and sulfuric and are described in detail in commonly assigned U.S. Pat. No. 4,315,763 which is incorporated herein. Briefly these novel liquid fertilizers are prepared by reacting from about 0.5 to 2 moles of urea with a mole of phosphoric acid or a mixture of phosphoric acid and from 5 to 80 weight percent sulfuric acid, in an exothermic reaction in the presence of less water than required to form aqueous solutions of the reaction products (i.e., urea phosphate and sulfate).
The reaction products are liquids which do not salt out at 0.degree. C. and which have pH of less than 4.
Although these compositions are stable, that is, they do not salt out or decompose rapidly, they do tend to suffer during storage from a decomposition of the urea portion of the composition, with a loss of acidity. As has been demonstrated, for example, in the U.S. Pat. No. 4,315,763, the acidity of the fertilizer, (hence the soil) greatly affects nitrogen loss from soil, i.e., nitrogen loss can be directly related to increasing pH. Thus it is highly advantageous to maintain the low pH which is obtained for the novel liquid fertilizer during even long periods of storage.
It is an advantage of the present invention that the high acidity of the described high analysis, nonammoniated, liquid fertilizer is maintained for longer periods of time. If is a further advantage that the decomposition of the urea phosphate and/or sulfates is inhibited. It is a particular advantage that the inhibitor is completely compatible in the compositions and in agricultural purposes. It is a further advantage that inhibiting can be obtained by addition of the inhibitor after the liquid fertilizers are manufactured. These and other advantages and features will become apparent from the following description.